1. Field of the Invention
The invention pertains generally to fuel management systems utilizing electromagnetic solenoid injectors and is more particularly directed to injector driver circuitry adapted for rapidly opening and closing the solenoid injectors of the system.
2. Prior Art
In the field of electronic fuel control systems, it is well known to provide a main electrical or electronic control unit (ECU) to generate electrical pulses of variable duration for ultimate control of an electromagnetic solenoid injector valve. The injector valve is connected to a source of pressurized fuel and is adapted to pass a stream of fuel to an associated engine injection point when opened in response to the variable duration pulses of the main computing means. Thus, the total amount of fuel injected for each actuation of the injector valve is function of the duration of the open time of the injector valve.
With the application of electronic fuel control systems to reciprocating piston internal combustion engines for automotive uses, the total available injector valve open time at high speed operation becomes a limiting operating factor with regard to total fuel injected. Thus, in order to maximize the quantity of fuel injected when the total available injector valve open time becomes minimized, it becomes essential that the electromagnetic injector valve be opened and closed as rapidly as possible so that the injector valve will be wide open for the maximum percentage of the time available for injection.
Main electronic computing circuits are readily adaptable to produce control pulses having nearly vertical leading and trailing edges and the capability of the electromagnetic injector valve to respond to, or follow, the control pulse thus becomes the limiting factor. Rapid valve opening times can be obtained by optimum design of the injector valve coupled with electronic or electrical circuitry to over-energize the valve but the closing time of the valve remains relatively slow due to the energy stored in the electromagnetic field. This is even a more significant problem when the injectors are energized in groups as the solenoids are then connected in a parallel configuration and store significantly more energy. It is, therefore, an object of the present invention to provide an improved electrical means of providing rapid dissipation of the energy stored in the electromagnetic field of the injector valve means.
The general problem described hereinabove has previously been recognized and partially solved, but the solutions proposed have been impractical from the standpoint of repeatability, size and cost. The previous solutions have proposed that an electrical oscillatory circuit be coupled with each independently actuated injector valve means to provide for more rapid dissipation of electrical energy. However, where such circuits are employed, it has been found that the commercially available capacitors, which may be combined with resistors and/or inductors to constitute the oscillatory circuit, will vary from their nominal value sufficiently during their operational life to render the valve closing time, and hence the quantity of fuel injected, indeterminate.
This has the end result of causing uncontrolled variations in the amount of fuel delivered to the associated engine. Furthermore, in fuel systems having two or more independently actuated injector valve means, it is possible to have slightly dissimilar valve closing characteristics between each independently actuated injector valve means and thus have fuel mixtures (and operational characteristics) which will vary from one injector valve means to the next. This may result in rough, uneven engine operation.
Another more advantageous solution to the problem is disclosed in a U.S. Pat. No. 3,665,899 issued to Nagy and commonly assigned with the present application. The disclosure of Nagy is hereby expressly incorporated herein by reference. Nagy teaches that a Zener diode connected to the solenoid coils of the injectors through a normally reversed biased diode can be used to dissipate the stored electromagnetic field in the injectors. The collapsing field of the injectors will cause a rapidly increasing negative voltage which will flow through the reversed biased diode and cause the Zener device to conduct once it exceeds the breakdown voltage of the device. The Zener device regulates the dissipation of the field by clamping the solenoid voltage to the Zener voltage and thereby causes a reproducible and rapid closing of the injector.
The closing times between different injectors can be normalized or made substantially identical with this method by connecting the solenoids in parallel and utilizing a common connection to a reversed biased diode. The closing times of different groups of paralleled injectors can also be normalized by using more than one reverse biased diode and providing as their common connection the terminal of the Zener device.
One drawback of this otherwise highly advantageous system is that all the energy stored in the collapsing electromagnetic field must be dissipated through the Zener device. Thus, when the closing times for groups of parallel injectors are normalized by this process, considerable energy is stored in the fields and a rather large power handling capability for the Zener is necessitated. Therefore, it would be desirable to decrease the amount of power the Zener device has to dissipate without adversely affecting the otherwise highly advantageous operation of this circuitry.